I think it's pointless arguing the Harem topic, it's beating a dead horse at this point. We know there won't be a romantic harem ending, at least not until after the game is complete, since it was mentioned maybe a bonus ending would be added afterwards.
We also know there will be romantic POLY endings, with like 2 or 3 girls, I doubt it will go beyond that considering the characters available. I'd say a poly relationship with 4 would be hopeful, and I'm struggling to think which 4 girls within the confines of the story so far would be willing to potentially partake in that sort of relationship. The only ones I can think of are Nicki, Mason, and likely Viola too. Some other potential but less likely candidates being Ashe and Brittani.
I get the feeling Gabby, Carolina, Madison, and Pepper are super unlikely to want a poly relationship, at least a romantic one. (Although Gabby and Viola throuple could be a thing... maybe) As far as Alex, Wren, Risa or Cassie go, we don't know much so no point in speculating on those four.
I think my dream poly ending would be, Nicki, Ashe, Mason, and Cassie. Since Ashe isn't likely though, I would settle for the other three.